This invention relates to window assemblies in which the frame and the sashes of each of the window units are constructed of extrusions, typically of rigid plastic or aluminum.
Extruded elements assembled to form window frames and sashes are disclosed in my U.S. Pat. No. 4,259,813 issued Apr. 7, 1981 for a Plastic Window and in my U.S. Pat. No. 4,640,048 issued Feb. 3, 1987 for a Window Sash Assembly. A double-hung window assembly is described in U.S. Pat. No. 4,259,813. U.S. Pat. No. 4,640,048 describes a lower window unit, known as an inner sash, that is vertically slidable and is also inwardly tiltable about a horizontal axis located at the lower rail of the sash.
In window assemblies of this type a significant design goal is to provide a unit that is light in weight yet is strong enough to withstand mechanical stresses without undue flexing and will provide good sealing against air and water leaks.